It is well known that the emissions performance of a diesel engine is largely determined by the pressure available to inject fuel into the engine cylinder. As engine emission standards become more stringent, extremely high fuel delivery pressures are required to satisfy the present and future emission regulations. For an engine having a fuel rail to supply the fuel to the injectors, the fuel is typically heated as it passes through the fuel rail which often extends through the cylinder head. Thus, the fuel injector closest to the inlet of the fuel rail typically gets the coolest fuel while the injector located at the distal end of the fuel rail receives fuel at a somewhat elevated temperature.
A prevailing design of fuel injection systems within the industry is to maintain the fuel injection duration, or pulse width of the fuel delivery signal, to be the same for all of the injectors across the fuel rail. However, because of the variation in fuel temperature at each injector, each of the fuel injectors along the fuel rail are subject to differing injection pressures. In other words, since the coolest fuel has a higher density and higher viscosity than the hottest fuel, the injector receiving the coolest fuel requires a higher injection pressure to inject a requisite fuel mass. Conversely, the hottest fuel has a lower density and viscosity, and thus, typically requires a slightly lower injection pressure to inject the predetermined mass of fuel.
Some of the related art devices have attempted to modify the pulse width of the fuel injector based on the desired fuel mass, the measured fuel density, the measured fuel viscosity, or any combination thereof. While it is well established that fuel density and viscosity are more or less related to fuel temperature, the related art devices merely adjust the pulse width for all injectors along a fuel rail by the same amount and do not compensate for the fuel temperature variations at each injector.
For example, U.S. Pat. No. 5,448,977 (Smith et al.) discloses a method for compensating fuel injector pulse width within an internal combustion engine based on the variations in injection pressure and temperature. Specifically, the fuel injector pulse width for all injectors is calculated as a function of desired fuel mass, injector pressure, in addition to the fuel temperature upstream of the fuel rail.
Similarly, U.S. Pat. No. 4,522,177 (Kawai et al.) discloses a temperature compensated fuel injection system that uniformly regulates the fuel supplied to the injectors based on the temperature of the coolant water or fuel. The fuel regulation is preferably accomplished by adjusting the pressure of the fuel supplied to the engine. Alternatively, Kawai et al. teaches that the injection time or pulse width can be adjusted. This pulse width adjustment is uniformly applied to all injectors and is apparently based on air intake quantity (i.e. intake pressures), engine speed, a feedback correction value, water temperature, air temperature, and fuel enrichment factors wherein the fuel enrichment factors are linearly related to fuel temperature.
Other related art devices include U.S. Pat. No. 5,474,054 (Povinger et al.), U.S. Pat. No. 4,252,097 (Hartford et al.), and U.S. Pat. No. 4,430,978 (Lewis et al.) all which disclose a fuel injector system that uniformly adjusts the pulse width of the fuel signal based on a variety of different inputs including a measured fuel temperature.
Disadvantageously, these related art devices do not compensate for the difference in fuel temperature in each of the injectors across the fuel rail. Rather, in the related art fuel injector systems that include a plurality of fuel injectors coupled along the fuel rail, the related art devices maintain a constant pulse width across those fuel injectors. The actual pulse width used in all injectors is based on a variety of different parameters or combinations thereof including desired fuel mass, injector response time, engine exhaust composition, measured pressure difference, average fuel density, or average fuel viscosity.